The present invention relates to a motor having supply brushes.
A number of technologies have been proposed to reduce abrasion of supply brushes used in direct-current motors, thereby extending the life of the brushes and the motors.
For example, high-resistance supply brushes reduce sparks generated at the supply brushes. Therefore, abrasion due to sparks is suppressed. This extends the life of the supply brushes.
However, high-resistance supply brushes create a great electrical power loss, which lowers the power of the motor.
To eliminate the drawback, Japanese Laid-Open Patent Publication No. 2002-119031 discloses a motor with a brush that has high-resistance portions and a low-resistance portion. The high-resistance portions are provided at a part of the supply brush that first contacts a commutator segment and a part that lastly separates from the segment. The remainder of the supply brush is the low-resistance portion.
Since the high-resistance portions of the supply brush suppress the generation of sparks, the life of the supply brush is scarcely reduced by abrasion. Further, the low resistance portion of the supply brush lowers the electrical resistance and suppresses electrical loss. This prevents the motor power from being lowered.
However, since the structure of the above described supply brush is complicated, the manufacture of the motor is burdensome and costly.
Particularly, when applying the technology of the publication to a motor having more than one set of two or more supply brushes, two or more brushes (for example, three or more brushes) in each set are anodes or cathodes, the cost will be undesirably increased.